Clean up a few unused functions, add a bit of static etc.

Clean up a few unused functions, add a bit of static etc.

Importantly:

The removal of the silly 'delete user script' behaviour when secuity=domain.

I have left the name the same - as it still does the (previously documented,
but not in smb.conf(5)) sane behaviour of deleting users on request.

When we decide what to do with the 'add user' functionality, we might
rename it.

Andrew Bartlett
(This used to be commit cdcfe3671eb7570e15649b77f708e6579055e7bc)